Isomerizing hydrocarbons



March 18, 1947. s. H. McALLlsTR ETAL 2,417,698

ISOMERI Z ING HYDROCARBONS Filed May 16, 1942 2 Sheets-Sheet l corccorusA EN COTECOIUEL TLQZNN my tou March 18, 1947. s, H, MCALLISTER ET Al.2,417,698

` ISOMERIZING HYDROCARBONS Filed May 16, 1942 2 Sheets-Sheet 2 ChzsrcrC. Crawford William E. |2055 bq 1m Mmmm.

Patented Mar. is, 1941 2,417,698 ISOMERIZIN G HYDROCARBONS Sumner Il.McAllister, Lafayette. Chester C. Crawford, El Cerrito, and William E.Boss, Berkeley, Calif., assignors to Shell Developnient Company, SanFrancisco, Calif., a corporation ofV Delaware Application May 16, 1942,Serial No. 443,268

(Cl. Mill-666) 13 Claims.

l This invention relates to the production of high octane paraihnichydrocarbon fractions from naphthenic petroleum fractions and relatesmore particularly to the production of multi-branched paraiiinhydrocarbons from naturally occurring hydrocarbon mixtures.

The aluminum halides are applied successfully on a practical scale tothe conversion of relatively pure parallin hydrocarbons, particularlybutane and pentane, to their respective branched chain isomers. Theapplication of these processes to the treatment of paraffin hydrocarbonshaving more than live carbon atoms -to the molecule is generally besetwith difficulties, however, due to .the diiliculty of obtaining thesehydrocarbons as relatively pure fractions. It is well known that theseparation on a commercial scale of hydrocarbon fractions consistingessentially of only a single paraffin hydrocarbon from many readilyavailable hydrocarbon mixtures, such as natural gas, petroleum, reneryproducts, etc., is often extremely impractical if not impossible. Thus ahexane or heptane fraction as obtained, for example, by thefractionation of natural gasoline, oftenv comprises substantial amountsof other hydrocarbons, particularly naphthenes, which because of theproximity of their boiling points to those of paraffin hydrocarbonshaving the same number of carbon atoms cannot readily be separatedtherefrom by practicallarge scale fractionating methods. At least asubstantial part of these naphthenes generally consist of naphthenes ofnon-hydroaromatic structure. The treatment of such fractions withaluminum halide catalysts in a single isomerization step in the absenceof substantial hydrocarbon decomposition produces a relatively smallrise in octane rating. Their treatment in accordance with methodsdisclosed heretofore furthermore generally produces only relativelysmall yields of the highly desirable multi-branched paraffinhydrocarbons, and attempts to increase the production in these processesof the multi-branched chain parafiins must generally be made at theexpense of shortened catalyst life.

In co-pending application Serial No. 443,269, filed May 16, 1942, it hasbeen shown that by the ing a mixture of these hydrocarbons tosuillciently mild isomerization conditions the naphthenes ofnon-hydroaromatic structure can be preferentially isomerized tonaphthenes of hydroaromatic structure in which latter form they can bemore readily removed from the admixed parafflns. Thisv improved method,although superior to those disclosed heretofore for the production ofhigh octane paraffin hydrocarbon fractions from naturally occurringhydrocarbon mixtures still does not enable .the conversion ofsubstantially all of the normal or single branched parafhns in thecharge to the highly desired multiremoval of naphthenes from theisomerization' charge to at least a substantial degree, marked increasein the octane rating of the product is obtained with considerableincrease in catalyst life. It has also been disclosed therein that inthe treatment of hydrocarbons with aluminum halide catalysts thereaction rates and response to variations in catalyst activity andoperating conditions of the naphthene and paraffin hydrocarbons differconsiderably, and that by subjectbranched chain paraffin isomers. By theterm hydroaromatic hydrocarbons as used throughout this specificationand claims is meant the naphthenes having a hexamethylene ring such as,for example, cyclohexane, the alkyl cyclohexanes, etc., to distinguishthem from naphthenes of nonhydroaromatic structure comprising thosehaving pentamethylene rings such as, for example, methyl cyclopentane,dimethyl cyclopentane, ethyl cyclopentane, etc.

It is an object of the present invention to provide an improved processfor the more efficient production of multi-branched chain paraffinhydrocarbons from naturally occurring hydrocarbon mixtures.

It is a further object of the invention to provide an improved processfor the more efficient conversion of straight and singly branched chainparaffin hydrocarbons in admixture with naphthene hydrocarbons ofnon-hydroaromatic structure and having the same number of carbon atomsto the molecule to multi-branched chainv paraffin hydrocarbons.

Another object of the invention is the provision of an improved processfor the more efficient production of dimethyl butane from commercialhexane fractions obtained by the fractionation of naturally occurringhydrocarbon mixtures such as, for example, natural gasoline. Otherobjects and advantages of the invention will become apparent from thefollowing detailed de-V scription thereof.

It has now been found that substantially increased yields ofmulti-branched chain paraiiin hydrocarbons and much greater catalystlife are obtainable in the isomerization of saturated hydrocarbons whenthe mixture is subjected to isomerization conditions of progressivelyincreased intensity. In a preferred embodiment of the invention thehydrocarbon mixture comprising, for example, paraflin and naphthenehydrocarbons of non-hydroaromatic structure,` is subjected to mildisomerization conditions effective to convert naphthenes ofnon-hydroaromatic structure of naphthenes of hydroaromatic structurethereupon removed from the resulting products of the mild isomerizationtreatment and the remaining hydrocarbons are subjected to a more severeisomerization in a second conversion zone wherein the reaction variablesare adjusted to produce predominantly single-branched paraiilnhydrocarbons rather than multi-branched paraiiin hydrocarbons. 'I'heresulting branched parain hydrocarbons are separated from the reactionproducts and subjected to isomerization conditions of preferably stillgreater intensity in a third conversion zone to convert less branchedparaffin hydrocarbons to more highly branched chain paraffinhydrocarbons.

In order that the invention may be more readily understood it will bedescribed herein with reference to the attached drawings formingpart ofthis specification and wherein:

Figure I illustrates more or less diagrammaticaliy one form of apparatussuitable for treating hydrocarbon fractions comprising paraiinhydrocarbons and naphthene hydrocarbons of non-hydroaromatic structurein accordance with the process of the invention and wherein thenaphthenes are recovered as suistantially pure hydroaromatic naphthenefractions, and

Figure II illustrates more or less diagrammatically a modified form ofapparatus, wherein all parts of apparatus identical'with those of FigureI are indicated with identical reference characters, suitable for thetreatment of hydrocarbon fractions comprising paraiiin hydrocarbons andnaphthene hydrocarbons of nonhydroaromatic structure in accordance withthe process of the invention, and wherein the naphthenes are recoveredin the form of relatively pure aromatic hydrocarbon fractions.

A mixture of saturated hydrocarbons comprising straight chain paraffinhydrocarbons and naphthene hydrocarbons of non-hydroaromatic structurehaving the same number of carbon atoms to the molecule, such as a hexanefraction boiling, for example, within the range of from about 45 C. toabout 85 C., comprising normal hexane, methyl cyclopentane andcyclohexane as obtained, for example, by fractionation of a naturalgasoline, is passed through valved line l, and heater 2, into aconversion zone. If the charge comprises substantial amounts of dimethylbutane and/or cyclohexane it may be subjected to a preliminaryfractionation by passage through valved line 3 into a feed fractionator4. Within fractionator 4 alight hydrocarbon fraction comprisingsubstantial amounts of dimethyl butane may be separated as a vaporfraction and eliminated therefrom through valved line 5. If substantialamounts of cyclohexane are present in the charge a heavier fraction, forexample, boiling above about 79 C. and comprising substantial amounts ofthe hydroaromatic naphthene hydrocarbon may be separated therefrom as aliquid fraction and withdrawn through valved line 6. The remainder ofthe charge comprising normal hexane and methyl cyclopentane, whichbecause of the proximity of their boiling points cannot be readilyseparated, and some cyclohexane, is taken from fractionator 4 throughvalved line 'l and passed into line I.

The conversion zone may comprise a reaction chamber 8 provided withsuitable stirring means. Within reactor 8 the hydrocarbons are subjectedto mild isomerization conditions whereby the nonhydroaromatic naphthene,methyl cyclopentane,

is converted to the hydroaromatic naphthene,

cyclohexane, as the predominant reaction. Suitable mildisomerizationconditions are maintained within reactor 8 by the use of a catalyst ofmild activity and/or a high ratio of hydrocarbon to catalyst, or a moreactive catalyst at a relatively low temperature with a high ratio ofcatalyst to hydrocarbon and short contact time. In a preferred method ofoperation the catalyst comprises a fluid catalyst of the molten salttype such as, for example, a molten mixture comprising aluminum chlorideand antimony trichloride, the activity of which has been reduced by usein the treatment of paramn hydrocarbons to a degree where the catalystpossesses but little if any ability to isomerize paraffin hydrocarbons.Thus it has been found that a catalyst of this type utilizedin theisomerization of hexane to a degree where isomerization of hexane was nolonger obtained, still possessed ability to isomerize naphthenehydrocarbons with equilibrium conversions. In the process of theinvention, a catalyst comprising a molten mixture of aluminum chlorideand antimony chloride which has been substantially spent in a paraiilnisomerizing step of the process as described more fully below, is passedinto reactor 8 through valved lines I0 and Il. When utilizing the moltensalt catalyst of reduced activity a temperature below 80 C. andpreferably not substantially above '75 C., and a phase ratio by volumeof catalyst to hydrocarbon in the approximate range of 1:5 to 1:10 havebeen found suitable. It is to be pointed out that hydrogen halides arepreferably present in only exceedingly small concentrations, forexample, in amounts below about 0.5 per cent by weight of thehydrocarbon charge to the reaction zone. Under these mild conditionssubstantial conversion of methyl cyclopentane to cyclohexane is obtainedas the predominating reaction, as'

shown by the following example.

Example I A mixture of normal hexane and methyl cyclopentane consistingof 81.5% by weight of normal hexane and 18.5% by weight of methylcyclopentane was treated at a temperature of 80 C. with a molten mixtureof aluminum chloride and antimony chloride, the activity of which hadbeen reduced by use in a previous hexane isomerization step until it hadbecome substantially spent with respect to paraiiin isomerization. Acontact time of '7.5 minutes and a ratio of catalyst to hydrocarbon of 1:5 by volume was maintained. A conversion of methyl cyclopentane tocyclohexane of 50% was obtained in continuous single-pass operation,whereas the maximum conversion of normal hexane to methyl pentaneattained only about 17.5%.

Although a catalyst comprising aluminum chloride and antimony chloridehas been selected as a suitable catalyst, it is to be pointed out thatother catalysts of the molten salt type, the activity of which has beenreduced, such as, for example, AlCla-NaCl-KCl; AlCls-NaCl-ZnClz;AlCla-ZnClz-SOz AlCla-NaCl-KCl-ZnClz etc., may be used. It is further tobe understood that catalysts which are inherently relatively mildisomerization catalysts such as, for example,

aumos actor 8 contains no more aluminum halide than that in molecularcombination 'with the hydrocarbon component of the catalyst and as suchis devoid of any substantial amount of free aluminum halide. It has beenfound that the hydrocarbon-aluminum halide complex compound itself does'not possess any appreciable ability to catalyze the isomerization ofparailin hydrocarbons, and that substantial paraiiln isomerization isobtained only by the suspension of free aluminum halide therein. Whenusing the aluminum chloride-hydrocarbon complex type catalyst, devoid ofany substantial amounts of free AlCla, somewhat higher temperatures, forexample, up to 100 C.,` preferably from about 60 C. to about 90 C., inthe presence of small amounts of a hydrogen halide promoter, forexample, below about 0.5% by weight of the charge, may be used. When acatalyst other than partially spent catalyst obtained in the process isused, such catalyst is introduced into the system through valved lineI2. The criterion for proper operating conditions within the firstconversion zone is mal hexane are passed overhead from fractionator 20through line 28 and heater 2l into a second conversion zone.'

Although but one reactor 8 is shown as constituting the rst isomerizingzone a plurality of reactors connected in series or parallel maysuitably be used. Additional fractionating means after the firstconversion zone. and between individual reactors thereof may be.resorted to in order to effect the separation of cyclohexane as well asa lighter fraction comprising some hexanes and unconverted methylcyclopentane which the preferential conversion of non-hydroaromaticnaphthenes to hydroaromatic naphthenes and the single factors comprisingtemperature, catalyst to hydrocarbon ratio and time of contact may varywithin the scope of the invention to obtain the desired mildisomerization conditions. Thus a more active catalyst may be used with alower temperature, or the use of a more active catalyst may becompensated for by the use of very low catalyst to hydrocarbon ratios asexemplified by the following example:

Example II A mixture of normal hexane and methyl cyclopentane consistingof 81.5% by weight of nor- Y mal hexane and 18.5% by weight of methylcyclopentane was treated with a molten mixture of aluminum chloride andantimony chloride at a temperature of 75 C. with a contact time of 5minutes and a ratio of catalyst to hydrocarbon of 1:18 by volume. Aconversion of methyl cyclopentane to cyclohexane of 53% was obtained,whereas only 19% of the normal hexane was converted to methyl pentane.

Eiiluence from reactor 8 comprising normal hexane, cyclohexane, andentrained catalyst is passed through line I3 into separator Il whereinseparation of catalyst and hydrocarbons is effected. Separated catalystis returned to reactor 8 through valved lines I8 and Il. After apericdof time the catalyst will lose its activity even for naphtheneisomerization. Spent catalyst is therefore withdrawn from the systemregularly or intermittently through line I6. The separated hydrocarbonsare passed through line I1 to a fractionator I8 wherein they aresubjected to fractionation together with isomerized hexanes from asubsequent stage of the process. A liquid fraction comprising normalhexane and cyclohexane is passed from the lower part of fractionator I8,through line I8 into a second fractionator 20 wherein a hydrocarboncomprising cyclohexane is separated as a liquid fraction and removedtherefrom through valved line 22 as a iinal product. If the charge tothe system is subjected to prefractionation in feed fractionator l, theheavier fraction removed through line 8 may be passed in part or in itsentirety through line 2| into line I8. Hydrocarbons comprising nor-- maybe recycled. It is apparent that by such means substantially all of thenon-hydroaromatic naphthenesare converted to the more readily re movablehydroaromatic naphthenes.

Paraiiln hydrocarbons consisting ,essentially of normal and singlebranched hexanes maybe introduced from an outside source through valvedThe second conversion" zone may comprise a reactor 26 or a plurality ofsuch reactors arranged in` parallel or in series. Within the reactor .28the hydrocarbons are subjected to conditions -of isomerization which aremore severe Vthan those maintained within the ilrst conversion zone.Heretofore the isomerization of such parafiin fractions for theproduction of high octane fractions has usually been effected underconditions most favorable to the formation of -multibranched chainparaflins. Such treatment in a single zone, it h as been found, resultsnot only in relatively shortened catalyst life but converts onlyrelatively small amounts of the normal paralns charged to themulti-branched chain isomers. In the process of the invention,conditions within reactor 26 are controlled to limit the formation ofmulti-branched parafflns and to produce primarily single branchedparafflns. This is eected by maintaining isomerizing conditions -oi.'intermediate severity by selection of proper temperatures, contact timeand catalyst to hydrocarbon ratio. A catalyst of high activity is used,however, in reactor 26. A particularly suitable catalyst comprises amolten mixture of aluminum chloride and antimony chloride. Othercatalysts of the molten salt type such as A1C13-NaC1-KC1AlCls-NaCl-ZnCla AICh-NaCI-KCl-Znclz AlCla--SOe--ZnCh and isomerizationcatalysts other than the molten salt type possessing high activity may,however, be used. 'I'he single factors comprising temperature, catalystto hydrocarbon ratio, time of contact and promoter content may varywithin the scope of the invention to obtain the isomerizationconditionsof intermediate severity the criterion of which is theconversion of normal parailins to branched'parafdns with a minimumproduction of multi-branched chain paraflin hydrocarbons. Suitableisomerizing conditions of intermediate severity when utilizing themolten salt type catalysts of high activity comprise temperatures in therange of from C. to 90 C.; a catalyst to hydrocarbon ratio -by volumefrom about 1:2 to about 1:5; a contact time in the range of from about 5to about 15 minutes; and the presence of a hydrogirhallde' promoter suchas hydrogen chloride, for example, in amounts ranging from about 2 toabout 10% of the charge. By

maintaining such conditions within the second conversion zone, hexanewill be converted to methyl pentanes with substantially increased cat-Example III A hexane fraction vconsisting predominantly of normal hexanewas treated with a catalyst consisting of a molten mixture of aluminum.chloride and antimony chloride at 85 C. with a catalyst to hydrocarbonratio of 1:1.7, contact time. of 16 minutes and the addition of 4%hydrogen chloride to the charge. 210 pounds of isomerizate having anincrease in octane rating of 20 umts over the charge were obtained perpound of aluminum chloride inthe catalyst, 23.3 pounds of neohexanebeing produced per pound of AlCla. A second portion of the same hexanefraction was treated with a molten mixture of aluminum chloride andantimony chloride under conditions minimizing the conversion of normalhexane to neohexane by reducing the temperature to 80 C., the catalystto hydrocarbon ratio to 1:5, the contact time to 4.5 minutes, and thehydrogen chloride addition to 2% of the charge. 548 pounds ofisomerizate, having an increase in octane rating of 21.5 units over thatof the charge, were obtained per pound of aluminum chloride in thecatalyst; only 13 pounds o'f n eohexane being produced per pound ofAlCla. An average conversion of normal hexane to methyl pentanes of 46%was .line 34. A part or all of the lighter fraction passing through line34 is recycled through line 35 intoV line 23. Make-uphydrogen halidepromoter is introduced from an outside source into line 35 by lmeans ofvalved line 36. 'I'he conversion within the second conversion zone maybe effected in the presence of diluent gases or agents such as hydrogen,isobutane or the like, capable of suppressing hydrocarbon decomposition.These may be introduced into line 35 from an outside source throughvalved line 3".

A hydrocarbon fraction comprising methyl pentane and unconvertedlvnormal hexane is obtained when continuing the operation under y theless severe conditionsl to a nal conversion of normal hexane to methylpentane of 14%.

The disadvantage of attempting to isomerize naphthenic hydrocarbonfractions in a single conversion zone, and more particularly theadvantage obtained by removing naphthenes from the charge to the secondconversion zone of the process, is illustrated by the following examplesshowing the eiect of increased naphthene concentrations in the chargeupon the eillciency of the conversion operation in terms of increase inoctane rating of the product over the charge.

Example IV Octane Weight per cent methyl cyclopentane in feed numberincrease of product Eiiluence from reactor 26 comprising methyl pentane,unconverted hexane, hydrogen halide promoter and entrained catalyst ispassed from passed from the lower part of fractionator 33 through valvedline 39 into fractionator I8 to be fractionated therein. A hydrocarbonfraction comprising methyl pentane is separated within fractionator i8and passed therefrom through valved line 4|. If desired, a part or allof the products passing through line 4| may be Aremoved from the systemas a flnal product through valved line 43. The methyl pentanes are,however, preferably passed through line 4I and heater 42 into a thirdconversion zone. The third conversion Zone may comprise a reactor 44provided with suitable stirring means, or a plurality of such reactorsarranged in series or in parallel.

Within reactor 44 the methyl pentanes are subjected to catalyticisomerization conditions favorable to their conversion to dimethylbutane. Isomerization conditions of greater severity than those in thesecond conversion zonel are preferably maintained within reactor 44.'Suitable catalysts comprise isomerization catalysts of high activitysuch as those described above for use ln the second conversion zone.Proper conditions are obtained by increase in one or several of thefactors comprising temperature, time of contact, catalyst to hydrocarbonratio,.or hydrogen chloride promoter content over those maintained inreactor 26. The following example illustrates the Example V Methylpentane was treated with a molten mixture comprising 92.5% by weight ofSbCls and 7.5% by weight of AlCla at a temperature of C. with a contacttime of 30 minutes and a ratio of catalyst to hydrocarbon of 1:5 byvolume. Hydrogen chloride and benzene in amounts of 2.5 and 1.1% byWeight respectively of the methyl pentane charge were introduced intothe reactor. A conversion ol.' methyl pentane to dimethyl butane of37.4% was obtained.

Excessively high temperatures at which substantial hydrocarbondecomposition is obtained are, however, avoided within reactor 44. Thuswhen utilizing the molten salt type catalyst, temperatures in the rangeof from about 80 C. to about C., and preferably from 80 C. to 95 C., arefound suitable.

lEiiluence from reactor 44 comprising dimethyl butane. unconvertedmethyl pentane and hydrogen halide is passed through line 4l intoseparator 48 wherein separation of catalyst from hydrocarbons iseffected. Separated catalyst is returned through'valved lines 41 and 48to reactor 4 4. Fresh catalyst is introduced into reactor 44 from anoutside source by means of valved line 49. Hydrocarbons and promoter arepassed from separator 48 through line 5I into a stripping co1- umn 62.Within column 52 a lighter fraction comprising hydrogen halide isseparated and removed overhead through valved line 58. A part or all ofthe material passing through line 53 is recycled through 4line 54'intoline 4I. Make-up hydrogen halide is introduced into line 54 from anoutside source through valved line 55. A diluent gas or an agent capableof 'suppressing hydrocarbon decomposition such as hydrogen, isbutane,benzene, etc., may be used in the third conversion zone, and isintroduced into line 54 from an outside source through valved line 56. Ahydrocarbon fraction comprising dimethyl butane and methyl pentane ispassed from column '52 through line 51 into fractionator 58. Withinfractionator 58 a hydrocarbon fraction comprising dimethyl butane isseparated and removed overhead therefrom through valveddine 59 as thenal product. A liquid fraction comprising unreacted methyl pentane andsome normal hexane formed within reactor 44 is separated Withinfractionator 58 and passed therefrom through valved line 6| into line 39leading to fractionator I8 A part of lthe hydrocarbons flowing throughline 6i may be recycled through valvedline 62, to aid in suppressing theformation of normal hexane within reactor 44.

When molten salt type catalysts are used in reactors 26 and 44. and amolten salt type catalyst of reduced activity is used as the catalyst inreactor 8` the catalyst which has become at least partially spent withrespect to paraflln isomerization and which is withdrawnfrom separators28 and 46 through lines 29` and 41, respectively, is passed in'part orin its entirety through valved lines l and il into reactor 8. After aperiodof use in reactor 8 the molten salt catalyst will become inactiveeven forthe isomerization of the non hydroaromatic naphthenes. Suchspent catalyst is removed from separator I4 through valved line I6. In apreferred method of executing the process of the invention, at least apart of the spent catalyst passing through line I6 is passed throughvalved line' 64 into the upper part of a scrubber 65. Within scrubber 65the spent catalyst is contacted countercurrently witha part or all ofthe hydrocarbon stream, in the liquid state, flowing through line 23. Tothis effect a valved line is provided leading from line 66 into anintermediate part of scrubber 65. Within scrubber 65 the more solublecatalyst components, which in the case of the AlCla-SbCla catalyst willcomprise SbCla, is recovered from the spent catalyst by solution in thehydrocarbon. The hydrocarbon stream comprising dissolved catalyst com-'lhe particular steps by which the hydroaro- I matic naphthenehydrocarbons are removed from the products emanating from the iirstconversion zone may vary within the scopeof the invention. Thus thisphase of the process may comprise, besides fractionation, one or more ofsuch steps as dehydrogenatin, solvent extraction, extractivedistillation, hydroforming, etc. Whereas in the treatment of anaphthenic hexane fraction, fractionationis found to be highly suitable,this method is often rendered impracticalwith hyrocarbon fractionscomprising hydrocarbons of more than six carbon atoms to the moleculeldue to the" complexity of the hydrocarbon mixture and the proximity ofthe boiling points of certain of the hydroaromatic naphthenehydrocarbons to those of the parailin constituents. Thus, vin thetreatment of a naphthenic hydrocarbon fraction comprising hydrocarbonshaving, for example, seven carbon atoms to the molecule, the products ofthe rst conversion zone comprise the hydroaromatic naphthene, methylcyclohexane, the boiling point of which differs by only about twodegrees from that of the normal heptane admixed therewith. Y

When treating a naphthenic hydrocarbon fraction comprising hydrocarbonshaving more than six carbon atoms to the molecule, theV removal of thehydroaromatic naphthenes from the products emanating from the naphtheneisomerizing zone may comprise such steps as the conversion I -of thehydroaromatic naphthenes to aromatic hydrocarbons, and the separation ofthe resulting aromatics by solvent extraction, extractive distillation,or othernsuitable methods. Thus, referring to Figure lI, a mixture ofsaturated hydrocarbonsconsisting essentially of yparailins andcycioparaillns of non-hydroaromatlc and hydroaromatic structure havingmore than six carbon atoms to the molecule such as, for example, aheptane fraction having a boiling range from about 85 C. to about 105C., comprising normal ponents is passed from scrubber through valvedline 61 back into line 23. Spent catalyst consisting essentially of acarbonaceous aluminum chloride-containing material settles to the lowerpart of scrubber 65 and is removed therefrom through valved line 68. Thetemperature to be maintained Within scrubber 65 will depend upon thenature of-the spent catalyst introduced therein. In general, atemperature in the range of from C. to 90 C. has been found suit-v ableand may be maintained therein by use of a suitable heat exchanger 69.

heptane, dimethyl cyclopentane, ethyl cyclopentane and methylcyclohexane, as obtained by fractionation of a naphthenic straightrungasoline, is introduced into the system through line i. If the chargecontain but a minor amount of ethyl cyclope'ntane and substantialamounts of methyl cyclohexane, it may be desirable to subject the chargeto a preliminary fractionation in fractionator 4 to separate a heavierfraction predominating in methyl cyclohexane as a bottom fraction, whichis withdrawn through line 6.

The Vremainder of the charge comprising substantially all of the normalheptane and dimethyl cyclopentanes is passed as a side stream fromfractionator 4 through lines 1 and l into reactor 8. Within reactor 8the hydrocarbons aretreated as described above to selectively convertthe non-hydroaromatic naphthenes comprising the methyl cyclopentanes andethyl cyclopentanes to hydroaromatic naphthenes comprising methylcyclohexanes. The products from reactor 8 comprising normal heptane andmethyl cyclohexane are passed through line l1 into a dehydrogenatingzone. If the charge to the system is subjected to a. pre-fractionationin feed fractionator 4, the heavier fraction removed through line 6 Imay be passed in part or in its entirety through line 10 into line l1.

The dehydrogenating zone may comprise a reactor 1l or a plurality ofreactors connected in series or in parallel. Within reactor 1I thehydrocarbon stream is contacted with a. catalyst under conditions atwhich the hydroaromatic naphbons.

. ence of added hydrogen.

thenes will be converted to aromatic hydrocar- It is preferred to use acatalyst of the nickel-tungsten-sulfur type, which it has recently beenfound is particularly eife'ctive in selectively converting hydroaromaticnaphthenes to aromatic hydrocarbons. The invention, however, is notlimitedto the use of this preferred type of catalyst, and otherdehydrogenation catalysts comprising, for example, chromium oxide ormolybdenum oxide on alumina or zirconia may be used.

The dehydrogenation is effected at a temperature in the range of, forexample, from about 400 C. to about 550 C., preferably at elevatedpressures, for example, above about 350 pounds, in the pres- The desiredtemperature conditions are maintained within reactor 1| by means ofheater 12 and if desired by other means, not shown -in the drawing, forsupplying heat from an outside source.

Products from reactor 1I comprising parai'iln and aromatic hydrocarbonsincluding, for example, normal Aheptane and toluene. are passed throughline 13 to an extractive distillation column 14 wherein they areextractively distilled in the presence of a suitable solvent havingpreferential solvent power for the aromatic hydrocarbons. Suitablesolvents comprise, for example, one or a mixture of the following:phenol, cresylic acids, alkyl phenol mixtures, etc. Bottoms from column14 comprising solvent and aromatic hydrocarbons arepassed through line15 to a distillation column 16 wherein aromatic hydrocarbons comprisingtoluene are separated from the solvent. Aromatic hydrocarbons comprisingtoluene are removed as overhead from column 16 through valved line 11 asa final product. The lean solvent is returned from column 16 to theupper part of column 14 by means of line 18.

Overhead from column 14 comprising parafilnic C1 hydrocarbons is passedthrough line 19 into fractionator I 8. 'I'hence the paramnichydrocarbons are treated as described above at isomerizing conditions ofprogressively increased intensity to obtain multi-branched parailinhydrocarbons having seven carbon atoms to the molecule as the finalproduct. Paramn hydrocarbons consisting essentially of normal and singlybranched heptanes may be introduced into line 19 through valved line 8|to be converted, together with the products emanating from fractionator14, to multi-branched chain heptanes. Such parafllnic hydrocarbonfractions may constitute at least a substantial part or even the totalhydrocarbon charge to the process. It has been found that the presenceof minor amounts of aromatic hydrocarbons such as benzene, toluene,etc., in the third conversion zone has the ability to suppressdecomposition of the branched chain paramns. Addition in amounts of, forexample, from about 1% to about 3% by weight of the charge to reactor 44have been found suitable. Higher or lower concentrations may, however,be used. The aromatic hydrocarbons may be introduced into the systemthrough line 56. When aromatics are obtained within the system as in themethod illustrated in Figure II,

' a part of such aromatics may be passed through valved line 80 directlyinto linel 4| carrying the charge to the third conversion zone.

The process of the invention is preferably executed in the liquid phase.Pressures sufllciently high to maintain at least a substantial part ofthe ,hydrocarbons being treated in the liquid phase are thereforemaintained within the conversion zones. v

The invention can be applied with particular advantage to the treatmentof hydrocarbon mixtures predominatlng in paramn and naphthenehydrocarbons having the same number of carbon atoms to the molecule,such as the fractions of relatively narrow boiling range readilyobtained by fractionation on a practical scale of naturally occurringnaphth'enic hydrocarbon mixtures, although it is to be pointed out thatthe invention is not necessarily limited thereto. Thus it is within thescope of the invention to treat naphthenic hydrocarbon fractionsofrelatively wider boiling range such as, for example, a fractioncomprising .the parailln and naphthene hydrocarbons of both six andseven carbon atoms to the molecule. The wider boiling fraction may besubjected to the ilrst conversion step of the process and the resultinghydrocarbon mixture subjected to a plurality of steps, not shown in thedrawing, which may comprise one or more such treatments asfractionation, solvent extraction, dehydrogenation, extractivedistillation, etc., to effect the separation oi' naphthenes fromtheparamns. Theresultingparamnfractions may then be subjected separatelyor combined to the other conversion steps of the process for theproduction of high octane parailln fractions predominating in branchedchain hydrocarbons. Oleilns, aromatic hydrocarbons and impurities whichare deleterious tov catalyst life are preferably removed to at least asubstantial degree from the charge by pretreatment which may compriseone or more of such steps as treatment with mineral acid, adsorbentclays, spent isomerization catalysts, etc. l

For the purpose of clarity, al1 parts of apparatus not essential to acomplete description of the invention such as, for example, pumps,condensers, accumulators, and the like, have been omitted from thedrawing. It is to be understood that the apparatus shown may be modifiedas apparent to one skilled in the art without departing from the scopeof the invention. Thus, for example, heaters 2, 24, 42 and 12 mayconsist of any suitable indirect heat exchanging means,

-fluid heaters comprising externally heated elongated coils positionedin furnace structures, or the like. In practical operation of theprocess of the invention, the hydrocarbon streams withdrawn fromseparators i4, 28 and 46 are preferably subjected to a fractionatingstep, by means not shown in the drawing, to remove entrained ordissolved catalyst components therefrom prior to their passage to anysubsequent part. of the system.

We claim as our invention:

1. Process for the production of dimethylbutane from hydrocarbonmixtures comprising normal hexane and methylcyclopentane which comprisescontacting the hydrocarbon mixture with a partially spent aluminumchloride-containing isomerization catalyst of the molten salt type in afirst conversion zone at a temperature not substantially in excess ofabout C. in the presence oi' an added hydrogen halide promoter notsubstantially in excess of about 0.5 per cent by weight of thehydrocarbon charge, thereby effecting the conversion ofmethylcyclopentane to cyclohexane as the predominating reaction,separating naphthenes comprising cyclohexane from the eiiluence of thefirst conversion zone, contacting the remaining hydrocarbons comprisingnormal hexane with an aluminum chloride-containing isomerizationcatalyst of the molten salt type in the presence of an added hydrogenhalide promoter in N a second conversion zone at a temperature in thehydrocarbon fraction predominating in methylpentane from the eiliuenceo! the second conversion zone, contacting -said methylpentane iractionin admixture with a hydrogen halide promoter with an aluminumchloride-containing isomerization catalyst of the molten salt type in athird conversion zone at a temperature in the range of from about 80 C.to about 125 C. and a time of contact sumciently long to effect theconversion of methylpentane to dimethylbutane as the predominantreaction, passing partially spent catalyst from the second and thirdconversion zones to the first conversion zone, and maintaining anincrease in at least one of the isomerizing conditions oi temperature,catalyst activity and time of contact in each of said conversion zonesover that maintained in each preceding conversion zone, therebymaintaining isomerizing conditions of progressively increased intensitythrough said conversion zones.

2. Process for the production `of multibranched paramn hydrocarbons fromhydrocarbon mixtures comprising straight chain parain hydrocarbonshaving at least six carbon atoms to the molecule and naphthenehydrocarbons of non-hydroaromatic structure having the same number ofcarbon atoms to the molecule which comprises contacting the hydrocarbonmixture with a partially spent aluminum chloride-containingisomerization catalyst of the molten salt type in a first conversionzone at a temperature not substantially in excess of about 80 C. in thepresence of an added hydrogen halide promoter not substantially inexcess of about 0.5 per cent by weight of the hydrocarbon charge,thereby effecting the conversion of naphthenes of non-hydroaromaticstructure to naphthenes of hydroaromatic structure as the predominantreaction, separating naphthenes comprising naphthenes of hydroaromaticstructure from the efiluence of the first conversion zone, contactingthe remaining hydrocarbons comprising straight chain parafiins with analuminum chloride-containing isomerization catalyst of the molten salttype in the presence of an added hydrogen halide promoter in a secondconversion zone at a temperature in the range of from about 80 C. toabout 90 C.. and a correlated contact time of from about to about 15minutes so as to effect the conversion of straight chain paraffins tosinglebranched paramns with a minimum formation of multi-branchedparains, separating a hydrocarbon fraction predominating insingle-branched parafiins from the eiliuence of the second conversionzone, and contacting said fraction predominating in single-branchedparaffins in admixture with a hydrogen halide promoter with an aluminumchloride-containing isomerization catalyst of the molten salt type in athird conversion zone at a temperature in the range of from about 80 C.to about 125 C. and a time of contact sufciently long to effect theconversion of single-branched parains to multibranched paraflins as the'predominant reaction, passing partially spent catalyst from the secondand third conversion zones to the first conversion zone, and maintainingan increase in at least one ofthe isomerizing conditions of temperature,catalyst activity and time of contact in each o! said conversion zonesover that maintained in each preceding conversion zone, therebymaintaining isomerizing conditions of progressively increased intensitythrough said conversion zones.

3. Process for the production of multibranched parailin hydrocarbonsfrom'hydrocarbon mixtures comprising straight chain paraffinhydrocarbons having at least six car-bon atoms to the molecule andnaphthene hydrocarbons of non-hydroaromatic structure having the samenumber of carbon atoms to the molecule, which comprises contacting thehydrocarbon mixture with a partially spent aluminum halide-containingisomerization catalyst of the molten salt type in a ilrst conversionzone at a temperature not substantially in excess of about C. Vin thepresence of ari added hydrogen halide promoter, thereby effecting theconversion of naphthenes of non-hydroaromatic structure to naphthenes ofhydroaromatic structure as the predominant reaction, separatingnaphthenes comprising naphthenes of hydroaromatic .structure from theeiiiuence of the rst conversion zone, contacting the remaininghydrocarbons comprising straight chain paramns with an aluminumhalide-containing isomerization catalyst of the molten salt typein thepresence of a hydrogen halide promoter in a second conversion zone at atemperature in the range of from about 80 C. to about C., limiting thetime of contact of hydrocarbons and catalyst in the second conversionzone so as to eect the conversion of straight chain paraflins tosingle-branched parans with a f minimum formation of multi-branchedparafins,

separating a fraction predominating in singlebranched paraffins from theaffluence of the second conversion zone, contacting said fractionpredominating in single-branched paraffins in admixture with a hydrogenhalide promoter with an aluminum halide-containing isomerizationcatalyst of the molten salt type in a third con-f version zone at atemperature in the range of i from about 80 C. to about 125 C. and atime of contact sufficiently long to effect the conversion ofsingle-branched parafns to multibranched parains as the predominantreaction, passing partially spent catalyst from the second and thirdconversion zones to the first conversion zone, and maintaining anincrease in at least one of the isomerizing conditions of temperature,catalyst activity and time of contact in each of said conversion zonesover that maintained in each preceding conversion zone, therebymaintaining isomerizing conditions of progressively increasedintensitythrough said conversion zones,

4. Process for the production of multibranched parain hydrocarbons fromhydrocarbon mixtures comprising straight chain paraflin hydrocarbonshaving at least six carbon atoms to the molecule and naphthenehydrocarbons of non-hydroaromatic structure having the same number ofcarbon atoms to the molecule, which comprises contacting the hydrocarbonmixture with a partially spent aluminum halide-containing isomerizationcatalyst of the molten salt type in a first conversion zone at atemperature not substantially in excess of about 80C. in the presence ofan added hydrogen halide promoter, thereby effecting the conversion ofnaphthenes of non-hydroaromatic structure to naphthenes of hydroaromaticstructure 'as the predominant reaction, separating naphthenes comprisingnaphthenes of hydroaromatic structure from the eiluence of the firstconversion zone, contacting the remaining hydrocarbons comprisingstraight chainpara'lns with an aluminum halide-containing isomerizationcatalyst of the molten s alt type in the presence of a hydrogen halidepromoter in a second conversion zone at a temperature in the range offrom about 80 C. to about 90 C., limiting the time of contact ofhydrocarbons and catalyst in the second conversion zone so as to eiectthe conversion of straight chain parafns to-single-branched parafns witha minimum formation of multi-branched parafiins, separating a fractionpredominating in singlebranched parafns from the eiiiuence of the secondconversion zone, contacting said fraction predominating insingle-branched p'arafiins in admixture with a hydrogen halide promoterwith an aluminum halide-containing isomerization catalyst of the moltensalt type in a third conversion zone at a temperature in the range offrom about 80 C. to about 125 C. and a time of contact suflciently longto eiect the conversion ofsingle-branched parains to multibranchedparans as the predominant reaction,

passing partially spent catalyst from the second and third conversionzones to the rlrst conversion zone, contacting spent catalyst drawn fromthe rst conversion zone with at least a portion of the charge to thesecond conversion zone, and maintaining an increase in at least one ofthe isomerizing conditions of temperature, catalyst activity and time ofcontact in each of said conversion zones over that maintained in eachpreceding conversion zone, thereby maintaining isomerizing conditions of-progressively increased intensity through said conversion zones.

5. Process for the production of dimethylbutane from hydrocarbonmixtures comprising normal hexane and methylcyclopentane, whichcomprises contacting the hydrocarbon mixture with an aluminumchloride-hydrocarbon complex catalyst substantially free of freealuminum chloride in a tlrst conversion zone at a temperature of fromabout 60 C. to about 90 C. in the presence o1' an added hydrogen halidepromoter not substantially in excess of about 0.5 per cent by Weight ofthe hydrocarbon charge, thereby effecting the conversion ofmethylcyclopentane to cyclohexane as the predominating reaction,separating naphthenes comprising cyclohexane from the efiiuence of therst conversion zone, contacting the remaining hydrocarbons comprisingnormal hexane with an aluminum chloride-containing isomerizationcatalyst of the molten salt type in the presence of a hydrogen halidepromoter in a second conversion zone at a temperature in the range offrom about 80 C. to about 90 C. and a correlated contact time oi.'l fromabout 5 to about l5 minutes so as to effect the conversion of normalhexane to methylpentane with a minimum formation of dimethylbutane,separating-a hydrocarbon fraction predominating in methylpentane fromthe eiiluence of the second conversion zone, contacting saidmethylpentane fraction in admixture with a hydrogen halide promoter withan aluminum chloride-containing isomerization catalyst of the moltensalt type in a third conversion zone at a temperature in the range offrom about 80 C. to about 125 C. and a time of contact sufciently longto effect the conversion of methylpentane to dimethylbutane as thepredominating reaction, and maintaining Aan increase in at least one ofthe isomerizing conditions of temperature, catalyst activity and timeo1' contact'in each of said conversion zones over that maintained ineach preceding conversion zone, thereby maintaining isomerizingconditions of progressively increased intensity through said conversionzones.

6. Process for the production of dimethylbutane from hydrocarbonmixtures comprising normal hexane and methylcyclopentane, whichcomprises contacting the hydrocarbon mixture with an aluminumchloride-hydrocarbon complex catalyst substantially free of freealuminum chloride in a rst conversion zone at a temperature of fromabout 60 C. to about 90 C. in the presence of an added hydrogen halidepromoter not substantially in excess of about 0.5 per cent by weight ofthe hydrocarbon charge, thereby effecting the conversion ofmethylcyclopentane to cyclohexane as the predominating reaction,separating naphthenes comprising cyclohexane from the eiiluence of thefirst conversion zone, contacting the remaining hydrocarbons comprisingnormal hexane with an aluminum chloride-containing isomerizationcatalyst of the molten salt type in the presence of a hydrogen halidepromoter in a second conversion zone at al temperature in the range offrom about C. to about 90 C., limiting the time of contact ofhydrocarbons and catalyst in the second conversion zone so as to effectthe conversion of normal hexane to methylpentane with a minimumformation of dimethylbutane, separating a fraction predominating inmethylpentane from the eilluence of the second conversion zone,contacting said fraction comprising methylpentane in admixture with ahydrogen halide promoter with an aluminum chloride-containingisomerization catalyst of the molten salt type in a third conversionzone at a temperature in the range of from about 80 C. to about C. and atime of contact suficiently long to effect the conversion ofmethylpentane to dimethylbutane as the predominating reaction, andmaintaining an increase in at least one of the isomerizing Aconditionsof temperature, catalyst activity and time of contact in each of saidconversion zones over that maintained in each 'preceding conversionzone, thereby maintaining isomerizing conditions of progressivelyincreased bon mixtures comprising straight chain parains having atleastsix carbon atoms to the molecule and naphthene hydrocarbons ofnon-hydroaromatic structure having the same number of carbon atoms tothe molecule, which comprises contacting the hydrocarbon mixture with analuminum halide-hydrocarbon complex catalyst substantially free of freealuminum halide in a first conversion zone at a temperature of fromabout 50 C. to about 100 C. in the presence of a hydrogen halidepromoter, thereby effecting the conversion of naphthenes ofnon-hydroaromatic structure to naphthenes of hydroaromatic structure asthe predominant reaction, separating naphthenes comprising naphthenes ofhydroaromatic structure from the eiiiuence of the first conversion zone,contacting the remaining hydrocarbons comprising straight chain parainswith an aluminum halide-containing isomerization catalyst of the moltensalt type in the presence of a hydrogen halide promoter in a secondconversion zone at a temperature in the range of from about 80 C. toabout 90 C., limiting the time of contact of hydrocarbons and catalystin the second conversion zone so as to effect the conversion of straightchain parans to singlebranched parafns with a minimum formation ofmulti-branched paramns, separating a fraction predominating insingle-branched parains from the emuence of the second conversion zone,con'- tacting said fraction predominating in singlebranched paralns inadmixture with a hydrogen halide promoter with an aluminumhalide-containing isomerization catalyst of the molten salt branchedparamn hydrocarbons from hydrocarbon mixtures comprising straight chainparailns having at least six carbon atoms to the molecule and naphthenehydrocarbons of non-hydroarov matic structure having thesame numberofcarbon atoms to the molecule, which comprises contacting the hydrocarbonmixture with an aluminum halide-hydrocarbon complex catalystsubstantially free of free aluminum halide in a rst conversion zone at atemperature of Vfrom about 50 C. to about 100 C. in the presence of ahydrogen halide promoter not substantially in excess of about 0.5 percent by weight of the hydrocarbon charge, thereby effecting theconversion of -naphthenes of non-hydroaromatic structure to hydrocarbonsof hydroaromatic 1- structure as the predominant reaction, separatingnaphthenes comprising naphthenes of hydroaromatic structure from theeilluence of the first conversion zone, contacting the remaininghydrocarbons comprising straight chain paramns with an aluminumhalide-containing isomerization catalyst of the molten salt type in thepresence of a hydrogen halide promoter in a second conversion zone at aparaffin isomerzing temperature below about 90 C., limiting the time ofcontact of hydrocarbons and catalyst in the second conversion zone toeffect the conversion of straight chain paraffins to single-branchedparafns with a minimum formation of multibranched parans, separating ahydrocarbon fraction predominating in multi-branched parans from theeiiluence of the second reaction zone, contacting said fractioncomprising multibranched hydrocarbons in admixture with a hydrogenhalide promoter with an aluminum halide-containing isomerizationcatalyst of the molten salt type in a third conversion zone at atemperature in the range of from about 80 C. to about 125 C. and a timeof contact sumciently long to effect the conversion of single-branchedparalins to multi-branched paraiins as the predominant reaction, andmaintaining an increase 1 in at least one of the isomerizing conditionsof temperature, catalyst activity and time of contact in each of saidconversion zones over thatmaintained in each preceding conversion zone,thereby maintaining isomerizing conditions of progressively increasedintensity through said conversion zones.

9. Process for the production o! dimethylbutane from hydrocarbonmixtures comprising normal hexane and methylcyclopentane which comprisescontacting the hydrocarbon mixture with an aluminum halide-hydrocarboncomplex cata- 18 lyst substantially free of free aluminum halide in afirst conversion zone under sufficiently mild isomerization conditionsto effect the conversion of methylcyclopentane to cyclohexane as thepredominating reaction, separating naphthenes comprising cyclohexanefrom the hydrocarbon mixture after the mild isomerization treatment,contacting the remaining hydrocarbons comprising normal hexane inadmixture with a hydrogen halide promoter with an aluminumhalide-containing isomerization catalyst of the molten salt type in asecond conversion zone at a paraffin isomerizing temperature below about90 C., limiting the timevof contact of hydrocarbons with the catalyst inthe'second conversion zone to effect the conversion of normal hexane tomethylpentane with a minimum formation of dimethylbutane, separating afraction predominating in methylpentane from the eiiiuence of the secondconversion zone, contacting saidfraction comprising methylpentane inadmixture with hydrogen halide with an aluminum halide-containingisomerization catalyst of the molten salt type in a third conversionzone at a temperature in the range of from about 80 C. to about 125 C.and a time of contact sufiiciently long to effect the conversion ofmethylpentane to dimethylbutane as the predominant reaction, andmaintaining an increase in at least one of the isomerizing conditions oftemperature, catalyst activity and time of contact in each of saidconversion zones over that maintained in each preceding conversion zone,thereby maintaining isomerizing con.-

ditions of progressively increased intensity through said conversionzones.

10. Process for the production of multibranched parain hydrocarbons fromhydrocarbone mixtures comprising straight chain paraflins having atleast six carbon atoms to the molecule and naphthene hydrocarbons ofnonhydroaromatic structure having the same number of carbon atoms to themolecule, which comprises contacting the hydrocarbon mixture with a mildisomerization catalyst comprising an aluminum halide in a rst conversionzone under sufficiently mild isomerization conditions to e'ect theconversion of naphthenes of non-hydroaromatic structure to naphthenes ofhydroaromatic structure as the predominant reaction, separatingnaphthenes comprising naphthenes of hydroaromatic structure from theeiliuence of the first conversion zone, contacting the remaininghydrocarbons comprising straight chain parafllns with a more activealuminum halide-containing isomerization catalyst in the presence of ahydrogen halide promoter in a second conversion zone at a paraflinisomerization temperature not substantially in excess of about C.,limiting the time of contact of hydrocarbons and catalyst in the secondconversion zone so as to effect the conversion of straight chain paramnsto singlebranched chain paramns with a minimum formation ofmulti-branched chain paraffins, separating a fraction predominating insingle-branched parains from the efiiuence of the second conversionzone, contacting said fraction comprising single-branched parafns inadmixture with a hydrogen halide promoter with a separate portion ofsaid more active aluminum halide-containing isomerization catalyst in athird conversion zone at a temperature of from about 80 C'. to about C.and a time of contact sufliciently long to eect the conversion ofsingle-branched parains to multi-branched parailins as the predominantreaction, and maintaining an increase in at leasty one of theisomerizing conditions of temperature, catalyst activity and time ofcontact in each of said conversion zones over that maintained in eachpreceding conversion zone, thereby maintaining isomerizing conditions ofprogressively increased intensity through said conversion zones.

1l. Process for the production of multibranched parafn hydrocarbons fromhydrocarbon mixtures comprising straight chain parafiins having at leastsix carbon atoms to the molecule and naphthene hydrocarbons ofnon-hydroaromatic structure having the same number of carbon atoms tothe' molecule, which comprises contacting the hydrocarbon mixture with amild isomerization catalyst comprising aluminum halide in a iirstconversion zone under suiciently mild isomerization conditions to effectthe conversion of naphthenes of non-hydroaromatic structure tonaphthenes of hydroaromatic structure as the predominating reaction,separating naphthenescomprising naphthenes of hydroaromatic structurefrom the eilluence of the first conversion zone, contacting theremaining hydro carbons comprising straight chain parafiins with a moreactive aluminum halide-containing isomerization catalyst in a secondlconversion zone under paraffin isomerizing conditions, limiting thetime of contact oi.' hydrocarbons and catalyst in the second conversionzone to effect the conversion of straight chain parafiins tosinglebranched parains with a minimum formation of multi-branchedparaflins, separating a fraction predominating in single-branched paransfrom the eluence of the second conversion zone, contacting said fractioncomprising single-branched parains with a' separate portion of said moreactive isomerization catalyst under parafiln isomerizing conditions inla third conversion zone, maintaining a time of contact in said thirdconversion zone suiciently long to 'effect the conversion ofsingle-branched parafiins to multibranched paraffins as the predominantreaction, and maintaining an increase in at least one of the'isomerizingconditions of temperature, catalyst activity and time of contact in eachof said conversion zones over that maintained in each precedingconversion zone, thereby maintaining isomerizing conditions ofprogressively increased intensity through said conversion zones.

12. Process for the production of dimethylbutane from saturatedhydrocarbons `comprising normal hexane which comprises contacting saidhydrocarbons in admixture with a hydrogen halide promoter in a iirstconversion zone with an isomerization catalyst comprising an aluminumhalide at a temperature in the range of from about 80 C. to aboutl 90 C.and a correlated.

contact time of from 5 to about 15 minutes so as to effect theconversionof normal hexane to methylpentane with a minimum formation ofdimethylbutane. separating a hydrocarbon fraction predominating inmethylpentane from the eluence of the first conversion zone, contactingsaid methylpentane fraction in admixture with a hydrogen halide promoterwith an isomerization catalyst comprising an aluminum halide in a secondconversion zone at a temperature in the range of from about 80 C. toabout 125 C. and

a time of Contact sufficiently long to effect the conversion ofmethylpentane to dimethylbutane as the predominant reaction, andmaintaining an increase in at least one of the isomerizing conditions oftemperature, catalyst activity and time of contact in said secondconversion zone over that maintained in the iirst conversion zone,thereby maintaining isomerizing conditions of progressively increasedintensity through, said conversion zones.

13. Process for the production of multibranched parain hydrocarbons fromsaturated hydrocarbons comprising straight chain paraiins having atleast six carbon atoms to the molecule which comprises contacting saidhydrocarbons in admixture with a promoter affording a hydrogen halide ina rst conversion zone with an isomerization catalyst comprising analuminum halide at a paran isomerizing temperature below about C. and acorrelated contact time of from about 5 to about 15 minutes so as toeect the conversion of straight chain parains to singlebranched parafnswith a minimum formation of multi-branched parains, separating ahydrocarbon fraction predominating in singlebranched parafns from theeiliuence of the iirst conversion zone, contacting said fractionpredominating in single-branched parains in admixture with a promoteraording a hydrogen halide with an isomerization catalyst comprising analuminum halide in a second conversion zone at a temperature in therange of from about 80 C. to about v C. and a time of contactsufficiently long to effect the conversion of singlebranched parains tomulti-branched parains as the predominant reaction, and maintaining anincrease in at least one of the isomerizing conditions of temperature,catalyst activity and time of contact in said second conversion zoneover that maintained in the rst conversion zone, thereby maintainingisomerizing conditions of progressively increased intensity through saidconversion zones. I

SUMNER H. McALLISTER.v CHESTER C. CRAWFORD. WILLIAM E. ROSS.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS v OTHER REFERENCES Schuit et al., Rec. Trav.Chem., vol. 59, 793-810 (1940).

Turova-Poliak et al., Comptes Rendus (Doklady) de lAcad. des Sciences delURSS (1941), vol. XDIII, No. 8, 551-4.

